Anesthesiology

Low CERVICAL-2 plane block, a proposed regional anesthetic technique for acute cholecystitis

a b s t r a c t

Introduction: acute cholecystitis is a painful inflammatory disease of the gallbladder. The Low Cervical-2 Plane Block is a retrolaminar block that targets the C3, C4, and C5 spinal nerves, which provide sensory innervation to the gallbladder, in order to potentially provide analgesia to patients with pain associated with acute cholecystitis.

Methods: In this brief report, a softly embalmed cadaver was injected with a dye mixture bilaterally. Results: Subsequent cadaveric dissection revealed spread of the injectate deep to the prevertebral fascia to the C4 lamina on the right side and the C5 lamina on the left side. Also, diffusion of the anesthetic over the ligamenta flava could spread inferiorly and laterally to the spinal nerve roots of C3-C5 and thus potentially target the direct sensory innervation of the gallbladder.

Conclusion: The Low Cervical-2 Plane Block is a potentially effective modality for treating intractable pain from acute cholecystitis. However, further cadaveric injections are needed to confirm the exact extent of spread of an- esthetic. Clinical application of the Low Cervical-2 Plane Block in patients with acute cholecystitis is needed to es- tablish the efficacy of this theoretical technique.

Introduction

Twenty percent of patients with symptomatic cholelithiasis (biliary colic) will progress to acute cholecystitis, making acute cholecystitis one of the most common causes of the surgical abdomen [1]. Prolonged contraction of the gallbladder in biliary colic induces vis- ceral pain, which patients sometimes experience as vague discomfort in the right shoulder due to shared sensory innervation of the gall- bladder (C3, C4, and C5 spinal nerves) and the Glenohumeral joint (C5 and C6 spinal nerves) [2]. Progression to acute cholecystitis (gallbladder wall inflammation and infection) results in peritoneal ir- ritation and more Intense pain localized to the right upper quadrant. Disposition to the operating room is often delayed by time to emergency department (ED) diagnosis, assessment by the surgical

* Corresponding author.

E-mail addresses: michael.shalaby@msmc.com (M. Shalaby), oarslan@fiu.edu (O. Arslan), oren.mechanic@msmc.com (O. Mechanic), anton.zitek@msmc.com (T. Zitek).

team, and subsequent OR planning. In one study, the median time from admission to OR was nearly 29 h [3]. Therefore, patients rou- tinely endure severe pain for significant amounts of time while awaiting surgery, and providing adequate analgesia to these patients while in the ED and after admission can be challenging.

In the ED, patients in severe pain from acute cholecystitis are gener- ally treated with opioids and non-opioid analgesics. However, opioids typically fail to completely eliminate pain from acute cholecystitis and can lead to complications such as respiratory depression, hypotension, and addiction [4]. Furthermore, while regional anesthesia techniques for addressing pain from acute cholecystitis have been documented- such as the transversus abdominis plane block and the Erector spinae plane block-these methods target pain sensation from the peritoneum, and not from the gallbladder itself [5,6].

To this end, we developed the “Low Cervical-2 Plane Block” on the hypothesis that anesthetic injected immediately inferior to the lamina of the 2nd cervical vertebra (C2) might diffuse inferiorly to anesthetize the C3, C4, and C5 spinal nerve roots, which provide sensory innervation to the gallbladder via the phrenic nerve [7]. Since there have been no previous publications regarding the use of the Low Cervical-2 block, we sought to inject a single cadaver with the goal of elucidating the

https://doi.org/10.1016/j.ajem.2023.06.011

extent of Anesthetic spread after the application of the Low Cervical-2 block.

Methods

To investigate our hypothesis, the primary author (MS) injected a cadaver with dye to simulate the extent of spread of anesthetic in a Low Cervical-2 block. A single softly embalmed cadaver preserved via the Thiel method, a technique designed to closely mimic living human tissue, was used [8]. We did not employ traditionally embalmed cadavers due to their inherent tissue stiffness and subsequent lack of deep tissue visibility on ultrasound.

To perform the Low Cervical-2 block, a linear array transducer is aligned with the cervical spine in the midline. After the spinous process of C2 is identified, the probe is moved slightly laterally until the lamina of C2 is visualized, keeping the probe oriented longitudinally adjacent to the spine (Fig. 1, Fig. 2). From an approach inferior to the probe tip, a spi- nal needle is directed toward the inferior aspect of the C2 lamina, and anesthetic is deposited. The nuchal ligament, which tightly adheres to the spinous processes and subcutaneous tissue, prevents the spread of anesthetic to the contralateral side [9]. Notably, this needle trajectory avoids the path of the vertebral artery, which does not emerge from the transverse foramina until superior to C2 (Fig. 3). The Low Cervical- 2 block was performed bilaterally to maximize the number of injections given the availability of a single freshly embalmed cadaver as well as to determine the variability of diffusion, if any, on both sides. The injectate consisted of 19 ml of normal saline and 1 ml of 1% Methylene blue, a robust human tissue dye that has previously been described in similar cadaveric anesthesia studies [10]. After injection, the spread of fluid was clearly visible on ultrasound (Fig. 4).

As a cadaveric study, this study does not meet the definition of human subjects research as defined in the Common Rule, and therefore, this study was exempt from institutional review board approval [11].

Results

One of the authors (OA), an experienced anatomist who has dissected over 1800 cadavers, led a posterior neck dissection four hours after injection to allow adequate time for the anesthetic to spread (Image 1). Using the course of the greater occipital nerve (dorsal ramus of the C2 spinal nerve) around the inferior capitis oblique muscles as a guide, the spread of dye was identified inferiorly to the laminae of C4 on the right and C5 on the left (Image 2).

Discussion

In this report, we have described the technique and simulated the extent of diffusion of anesthetic after a Low Cervical-2 block, a novel

Fig. 1. Ultrasound image of the lamina of the 2nd cervical vertebra.

Fig. 2. Demonstration of patient positioning, probe manipulation, and site and angle of in- jection of the Low Cervical-2 retrolaminar plane block. Transducer position is slightly lat- eral to midline, oriented in a longitudinal fashion to the cervical spine.

regional anesthetic technique. The recently developed cervical erector spinae plane block utilizes a similar technique that involves the injection of anesthetic at the transverse process of either C5 or C6 that diffuses superiorly and inferiorly to reach the spinal nerve roots. Limited case reports have demonstrated that the cervical erector spinae plane block simulates a brachial plexus block in efficacy [10,12-16]. The inves- tigators of the cervical erector spinae plane block performed a cadaveric study with methylene blue dye which demonstrated the extent of spread of dye to the roots of the brachial plexus [10]. The Low Cervical-2 block employs a target site of injection higher in the cervical spine than the cervical erector spinae plane block, making it a poten- tially effective modality for anesthetizing the higher nerve roots that in- nervate the gallbladder. As is seen in Image 2, injectate not only diffused inferiorly but also laterally. The C3-C5 spinal nerve roots emerge inferolaterally to the C2-C4 lamina, respectively, and thus it is possible that injected anesthetic may diffuse over the ligamenta flava and further laterally guided by the prevertebral fascia to the C3-C5 nerve roots.

Fig. 3. Vertebral artery exits its course through the transverse foramina cranial to the TP of C2, as it enters the foramen magnum. Blue arrow denotes the inferior aspect of the lamina of C2, the site of injection of the LoC2 block. Figure taken with permission from Essential Anatomy 5th Edition, 3D Medical.

Fig. 4. Ultrasound image of the lamina of C2 after injection with methylene blue dye. Arrow denotes the hypoechoic area (representing fluid) between the tip of the lamina and the erector muscle group.

As with any form of regional anesthesia, patient safety is paramount. The phrenic nerve, formed by the C3-C5 spinal nerve roots, is an indirect target of the Low Cervical-2 block and hence hemidiaphragmatic paral- ysis is likely. However, in healthy patients, blockade of the trunk or the

roots of the phrenic nerve may be of limited consequence. The interscalene nerve block, which targets the C5-C7 roots of the brachial plexus, frequently induces dense hemidiaphragmatic paralysis due to anesthesia of the C5 branch of the brachial plexus. Yet, patients catego- rized by the American Society of Anesthesia (ASA) as Class I-II status are less likely to desaturate or become dyspneic [17]. The cervical erector spinae plane block, which likewise anesthetizes the C5 nerve root, has also not been shown to make patients dyspneic, even when performed bilaterally [12-16]. In fact, direct phrenic nerve blockade has been uti- lized after hepatectomy and thoracic surgery to reduce post-operative shoulder pain [18,19], as well as for intractable hiccups [20]; notably, none of the participants in these studies displayed respiratory compro- mise. While patients with chronic cardiac or pulmonary conditions may not be ideal candidates for the Low Cervical-2 block, healthier patients will probably not experience Respiratory complications.

There are a few notable limitations of this report, including limited information on the efficacy and safety that can be derived from the in- jection of a single cadaver. In vivo, diffusion of anesthetic is more likely to be robust due to human movement, fascial plane sliding, and active physiologic processes, but is presumably more passive and limited in inert cadaveric tissue [21]. On the other hand, the softly embalmed ca- daver was a thin Elderly woman with lower body mass and thinner cer- vical soft tissue. The authors believe that these characteristics may have improved ultrasound visualization and potentially led to the improved diffusion of injectate. Furthermore, the disparity in the depth of diffu- sion of injectate on each side may have been secondary to the cadaver’s

Image 1. Incision and Injection sites.

Image 2. Extent of spread of methylene blue.

inherent tissue stiffness or to the site or angle of injection on each side. The true extent of anesthetic spread after a Low Cervical-2 block has yet to be clarified. Moreover, the exact sensory innervation of the gallblad- der remains to be elucidated. Therefore, the clinical efficacy of the Low Cervical-2 block, even with sufficient spread of anesthetic, may require further studies involving multiple cadavers and potentially even human subjects.

Conclusion

Pain from acute cholecystitis can be severe and protracted, and pro- viding adequate analgesia to patients poses a challenge for physicians. In our injection of a single cadaver with bilateral Low Cervical-2 blocks, we demonstrated that the injectate may spread to the level of the C3, C4, and even C5 spinal nerve roots. Safety parameters, the extent of spread of the anesthetic, and potential clinical efficacy remain unknown. Fur- ther studies should include more cadaveric injections or animal models.

CRediT authorship contribution statement

Michael Shalaby: Writing – review & editing, Writing – original draft, Supervision, Project administration, Methodology, Investigation, Conceptualization. Orhan Arslan: Writing – review & editing, Writing

– original draft, Supervision, Methodology, Investigation,

Conceptualization. Oren Mechanic: Writing – review & editing, Super- vision. Tony Zitek: Writing – review & editing, Supervision.

Declaration of Competing Interest

None.

The authors declare no competing interests. Support was provided solely from institutional and/or departmental sources.

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AJEM

Low CERVICAL-2 plane block, a proposed regional anesthetic technique for acute cholecystitis

a b s t r a c t

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